Melting away defects in microchip components

Material defects are are the bane of microchip manufacturers, but a process devised by engineers at Princeton University in New Jersey could literally melt them away.

With their densely packed electronic components, microchips work best when the structures are straight, thin and tall. Edge roughness and other defects can result in degraded performance through current leakage and voltage fluctuation.

Instead of trying to improve chip manufacturing methods, Stephen Chou and his graduate student Qiangfei Xia are looking to fix defects after fabrication. “Fixing the defects could be automatic – a process of self-perfection,” says Chou.

Direct heating has been shown to smooth out defects in plastic structures, but with the much higher melting point of silicon this approach will not work. Not only would it melt everything indiscriminately, it would also widen the widen the structures and round off their edges.

Chou and Xia have overcome the temperature problem by using pulses of light from an excimer laser, which heats only a very thin surface layer of material. If this is done for less than a microsecond, the structures melt and the liquefied material can be guided so that it re-solidifies into the desired shapes.

To retain the definition of the chip structures, Chou and Xia place a thin quartz plate on top of the melting structures to guide the flow of molten material. The plate prevents the structure from widening, and keeps its top flat and sides vertical.

“This self-perfection by liquefaction process is very reliable due to the micro/nanostoppers and air cushion press that we employed in our approach,” says Chou. “We mentioned but did not emphasise them, since the paper is about a new approach.”

The researchers plan next to demonstrate the technique on 8-inch wafers. According to Chou, several leading semiconductor manufacturers have already expressed an interest in the technique.

Figure: Electron microscope images show nanoscale structures on a semiconductor substrate before (left) and after (right) heating with sub-microsecond pulses of light from an excimer laser. The process could remove defects from microchips without damaging the electronic components (source: Stephen Chou/Princeton University).